Sleep disturbances are highly prevalent among people living with HIV (PLWH) and are associated with increased cardiometabolic risk, cognitive impairment and reduced quality of life. As antiretroviral therapy has transformed HIV into a chronic condition, understanding how sleep disruption may affect long-term health has become increasingly important. However, while sleep problems in PLWH are well documented, the mechanisms underlying these disturbances remain poorly understood. This thesis investigates whether HIV status is associated with differences in sleep timing, duration and circadian regulation in older adults living in a rural South African community. Chapter 2 characterises sleep timing, light exposure, chronotype and subjective sleep quality across younger urban and older rural adults. Among the rural population, sleep timing was closely synchronised to the natural light-dark cycle. However, individuals with chronic conditions, including HIV, reported more symptoms of insomnia. Focusing on the rural population, Chapter 3 presents physiological evidence of a significantly delayed and more variable circadian phase in PLWH, compared to those without HIV, as measured by dim light melatonin onset (DLMO). Sleep onset was also delayed and total sleep time was reduced in PLWH; however, sleep timing was not delayed proportionally with DLMO, resulting in a compressed or negative phase angle of entrainment – suggestive of circadian misalignment. Chapter 4 examines the utility of the Munich Chronotype Questionnaire (MCTQ) and the novel Perfect Day Questionnaire (PDQ) as behavioural proxies for DLMO. While overall chronotype did not differ by HIV status, PLWH reported earlier bedtimes, longer sleep on workdays and a steeper age-related advance in chronotype. This may reflect increasing fatigue with age, or altered circadian regulation. These findings offer the first human evidence that HIV may disrupt circadian rhythms and highlight the importance of researching sleep and circadian rhythms in ageing PLWH, especially in LMICs, to support a more equitable global research agenda.